This invention relates to a method of diversity reception of transmitted radio-frequency signals and to receivers for use in the method.
Diversity reception is a technique that has often been used, particularly for mobile reception of signals. Typically, it involves two (or more) receiving antennas, and some signal processing to combine the received signals. The two antennas are generally located so that they can receive different versions of the same transmitted signals. This may be done for example by placing them a short distance apart (antenna spatial diversity), or by using antennas with different polarisation (antenna polarisation diversity) or radiation pattern (antenna pattern diversity). Frequency diversity is also known in which the signal is transmitted on two frequencies; in this case a single antenna may suffice connected to two tuners.
U.S. Pat. No. 5,345,600 describes a time and frequency diversity system which uses re-transmission of signals in poor signal conditions and requires transmission from the xe2x80x98receiverxe2x80x99 back to the xe2x80x98transmitterxe2x80x99. European Patent Application EP-A-766 414 describes another transceiver using space and polarisation diversity, the manner of operation not being specified.
Strictly speaking, if the signal paths are such that only one of the antennas is capable of receiving a signal at any one time, then this is not a diversity system, but a system with extended coverage capabilities. However, such a system is regarded as being a diversity system within the meaning of the term as used in this specification. In any event, in practice it is likely that local reflections will always ensure that both antennas receive some signals.
The invention in its various aspects is defined in the independent claims below to which reference should now be made. Advantageous features are set forth in the appendant claims.
A preferred embodiment of the invention is described in more detail below with reference to the drawings. In this embodiment, designed in the context of broadcast COFDM signals, a diversity receiver for receiving digital signals has a soft-decision decoder in each of its receiving sections, to provide confidence values for the received decoded digital values, and combines the values from the receiving sections in dependence upon the confidence values. The receiver has two sections the outputs of which are applied to a soft-decision combiner which combines the signals in dependence upon confidence values received from the tuner/demodulators. The output is then applied to a Viterbi decoder. The combining can simply involve switching but preferably involves averaging. Synchronisation and squelching can be provided. The system can be used with frequency diversity, spatial or polarisation diversity, or with antenna pattern diversity, in which case it can constitute an automatic rotator. The system automatically selects from all possible diversity sources the two sources which provide the best quality signals.